Book/Report

FZJ-2018-03411

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Berechnung von Kräften und Gitterrelaxationen für Punktdefekte in Metallen

Abraham, K.FZJ* ; Drittler, B.FZJ* ; Zeller, R.FZJ* ; Dederichs, P. H.FZJ*

1991
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/18869

Report No.: Juel-2451

Abstract: The central aim of this report is the calculation of interatomic forces induced by impurities in metals, in particular in Cu, Ni and Pd. Force calculations are an important, but difficult problem in electronic structure calculations. The difficulty arises from the fact, that the standard expression for the force, as given by the Hellmann-Feynman theorem, requires a fully selfconsistent charge density. Contrary to the total energy, first order errors in the density lead to first order errors for the force since the extremal properties with respect to the charge density are lost. We review the different approaches presented in the literature how to deal with this problem. Especially we derive a force formula which is bas d on a spherical core approximation and which is insensitive against small variations of the core charge density. The present force calculations are based on this expression. The charge densities entering in the force calculations are determined within local density functional theory. We apply a recently developed full- potential KKR Green's function method and selfconsistently calculate the potential and charge perturbations for the impurity and for six shells of perturbed host atoms. Knowing the forces we use lattice statics in the harmonic approximation in order to estimate the lattice displacements of the neighboring host atoms, as well as the relaxation energy and the volume change induced by the defect. We compare our results with EXAFS data for the nearest neighbor displacements and with X-ray diffraction results for the volume changes. In general we obtain good agreement for impurities with small valence differences. For strongly disturbing defects the calculations overestimate the lattice relaxations. The possible sources of these errors are discussed. For non-magnetic impurities the calculated trends of the volume changes are reasonably well described by Vegard's law, whereas for magnetic 3d-impurities strong deviations are observed due to magneto-elastic effects.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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